The present invention relates to a short-range wireless communication system for conducting wireless communications over relatively short distances, as well as to a portable terminal apparatus and a wireless communication apparatus constituting that system.
Today, portable terminal apparatus (or simply called the terminal) typified by mobile phones are gaining higher functionality and greater versatility than ever before. Along with this trend has come the growing risk of getting the terminal misplaced or stolen, with the result that personal information or electronic purses kept therein could be pilfered or abused.
One proposed solution to the problems above involves having authentication data transmitted from a suitable wireless card or authentication card to the portable terminal so that the terminal is rendered usable only when authenticated by the transmitted data, whereby the abuse of the terminal by anyone other than its legitimate user can be prevented (as disclosed in Japanese Patent Laid-Open Nos. 2001-352579 and 2001-358827).
Another proposed solution to the above problems involves having either a transmitter or a receiver attached to a portable object while the other device is worn by the person carrying that object. When the intensity of radio waves received by the receiver from the transmitted drops below a threshold, an alarm is activated (as disclosed in Japanese Patent Laid-Open No. Hei 8-214933).
Recent years have seen the emergence of portable terminals with short-range wireless communication capabilities such as Bluetooth (registered trademark) for conducting wireless communications over relatively short distances. These terminals are used illustratively in wireless communication with a headset that allows the user to place a call in hands-free fashion, or are arranged to execute data communications with personal computers (PC).
It is conceivable to devise an alarm system getting the user to wear a portable wireless communication apparatus for wirelessly communicating with the short-range wireless communication facility of the terminal apparatus. With this system, an abnormal drop of a signal reception level (e.g., disconnection) during the communication monitored between the user-worn device and the terminal triggers an alarm that will alert the user to the imminent misplacement or theft of the portable terminal.
How to activate such an alarm system poses a problem: the power of transmission is typically adjusted in keeping with the level of signal reception which varies in a changing communication environment between the two devices communicating at close range. As the transmission power is gradually raised to compensate for the drop in the reception level over growing distances between the two device, a breakdown of communication can take place only after a considerable distance has been traveled (e.g., 100 meters at worst). If an alarm is activated at that point to alert the user to the portable terminal being misplaced, going back to recover it over such a long distance can take the user time and trouble that is not negligible. In case of a theft, the alarm activated with such a long distance already traveled makes retrieving the stolen object all but impossible.
Another problem with the above system is that the distance between the two devices (called the working distance) at which the alarm is triggered due to the breakdown of communication can be considerably uneven. That is because the radio waves with frequencies for short-range wireless communications (e.g., on the 2.4 GHz band) are easily affected by the presence of human bodies. The alarm can be triggered at distances of 5 meters or 50 meters. This can give rise to further complications in implementing the system.
The present invention has been made in view of the above circumstances and provides a portable terminal apparatus, a wireless communication apparatus, and a short-range wireless communication system for reducing unevenness of the working distance at which to alert a user to an unusual distance incurred between the portable terminal apparatus and the wireless communication apparatus, or beyond which to limit the use of some functions of the portable terminal apparatus.